A lawyer who gave evidence to the parliamentary committee investigating press behaviour, today called on Baroness Buscombe, the chair of the Press Complaints Commission, to resign. He claimed she had published what were termed "extremely serious" false allegations against him.

Solicitor Mark Lewis earlier this year, in testimony to the House of Commons culture, media and sport select committee, gave an account of a conversation he had with police, alleging that "thousands" of people were targeted by phone hacking.

Buscombe claimed at the weekend that police had been misquoted in oral evidence to the committee. She said: "Any suggestion that a parliamentary inquiry has been misled is of course an extremely serious matter."

In a letter to Buscombe and to the chairman of the parliamentary committee, Lewis said today: "You have betrayed any semblance of impartiality and regrettably ought to find yourself in a position where the honourable action would be for you to resign."

He said the discussion he had with Det Sgt Mark Maberley, from the team investigating the tabloid's behaviour, had been witnessed by two others, including a barrister who was acting for his client at the time, one of the paper's victims. Maberley told him there were 6,000 instances of phone hacking, although only one case had been prosecuted, involving the royal reporter Clive Goodman, who subsequently went to jail.

"I am deeply concerned that you have thought it proper to criticise my evidence to the select committee without either having the courtesy or the propriety to put the allegations to me first," said Lewis. "I regret that your failure to act properly has compromised any veneer of impartiality that you sought to create."

Buscombe said she received a letter from Metropolitan police lawyers, which she did not publish or quote directly. She claimed that it said Maberley, who has not testified either to the PCC or to the parliamentary inquiry, was "wrongly quoted".

She delivered her allegations while seeking to defend the Press Complaints Commission, which she chairs, at a weekend speech to the Society of Editors. The allegations were held back from a previously circulated text of her speech, and then issued as a public statement at short notice last night. She reportedly told one newspaper: "One of my challenges is to show the public we are not in the pockets of the press."

The PCC has been facing accusations of a whitewash, since it refused to accept new evidence supplied to the parliamentary committee by the Guardian and others, which alleged the News of the World was involved in more instances of phone hacking than merely the Goodman case. In a recent statement, the PCC denied that it had been "materially misled" by accepting previous assurances from the News of the World that Goodman had "acted alone".

Witnesses criticised the PCC for its inability to uphold press standards during the parliamentary inquiry, which is expected to report imminently. It is chaired by the Conservative MP John Whittingdale.

The links between the Rupert Murdoch-owned News of the World and the Conservative party have recently strengthened. Andy Coulson, the editor of the News of the World at the time of the phone-hacking, is currently the media adviser to Tory leader David Cameron. The Murdoch tabloids have now declared political support for Cameron. Buscombe, the recently-appointed PCC chair, is a Conservative peer and former front-bench spokesman on the media.

A Guardian spokesman said today: "It is surprising that the PCC should have publicly questioned the evidence a solicitor gave to MPs without even doing him the courtesy of contacting him to seek his version of events.

"It turns out Mr Lewis's account contradicts the hearsay evidence attributed to Det Sgt Maberly. Why did the PCC never contact Mr Lewis – either before writing its report or after hearing from the police? Such behaviour from a regulator can only be regarded as erratic."

A spokesman for the Press Complaints Commission said: "I don't think to call for her resignation is calm or reasonable.

"Our statement was based on a follow-up piece of information that we received. We made clear that is what happened and said we could consider it. It was a perfectly legitimate and reasonable thing for us to have done."

He added: "We would like to emphasise that if you read the statement [Baroness Buscombe] has not accused Mr Lewis of anything. It is a factual statement, a piece of evidence that we received and we have merely made it public in an open fashion and said we were going to consider it.

"The PCC has not made any accusations against Mr Lewis or anyone else."

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